1. Field of the Invention
The present invention relates to an auxiliary agent for sintering ceramic materials and, more particularly, an auxiliary agent for sintering dielectric ceramic materials.
2. Description of the Prior Art
In general, ceramic dielectrics mainly comprising barium titanate (BaTiO.sub.3), or strontium titanate (SrTiO.sub.3), or titanium oxide (TiO.sub.2) or the like have widely been used for production of monolithic ceramic capacitors. Such monolithic ceramic capacitors are generally built up of an arrangement of alternating two layers of a dielectric ceramic layer and an internal electrode layer and are produced by preparing ceramic green sheets, forming a layer of metal paste for internal electrodes on each ceramic green sheet, stacking them and firing the resultant stacked body at a temperature of 1300.degree. C. and above. It is therefore required to use a high-melting noble metal such as platinum-palladium as a material for internal electrodes to prevent from oxidation.
However, the noble metals are expensive and occupy a greater part, generally about 30 to 50%, of the production cost of monolithic ceramic capacitors. Thus, the use of the noble metal sets a limit to reduce the production cost of the monolithic ceramic capacitors. In addition, a sintering furnace is considerably damaged at high sintering temperatures of not less than 1300.degree. C., resulting in increase of maintenance cost of the furnace with the operating time being elapsed. Further, the sintering at high temperatures results in considerable increase of the energy cost required for production of monolithic ceramic capacitors.
To solve such problems, it has been proposed to use a lead-containing dielectric ceramics with a low-sintering temperature or nonreducible dielectric ceramics, as a material for capacitors. These ceramic materials make it possible to use cheap metals such as nickel as a material for internal electrodes of the monolithic capacitors. Also, attempt has been proposed to produce monolithic ceramic capacitors by a process comprising the steps of preparing multilayer sintered ceramic bodies with plural spaces between adjacent ceramic layers, pouring a molten metal such as lead or a lead-tin alloy into each space to form internal electrodes, and cooling the same to solidify the molten metal. However, such new dielectric ceramic materials have some disadvantages awaiting a solution.
On the other hand, the dielectric ceramic compositions of the prior art have excellent dielectric properties required for production of ceramic capacitors including monolithic ceramic capacitors. Thus, if the dielectric ceramic compositions of the prior art can be sintered at low sintering temperature, there is no need to use the above new dielectric ceramic materials.